64 INS 



the Staphyitnidae, &c. Insects which, on the con- 

 trary, have the abdomen short, and especially those 

 in which it is defended by the wing-covers, possess 

 but very little power of motion in this part of the 

 body. "Another circumstance, also, has much influ- 

 ence in the same respect ; when the segments of 

 the abdomen simply touch each other at the margins, 

 the motion is very limited ; but in those which have 

 the abdominal wings formed to slide into each other, 

 the motion is much more exteusive. 



The organs of generation (with the exception of 

 those of the male, LibcllidoE, which are placed be- 

 neath the h'rst abdominal segment), are situated at 

 the extremity of the abdomen. 



The stinj: (acxleus), and the ovipositor (ovidnc- 

 tut), are the onfy instruments connected with these 

 organs which it will be convenient to notice in a 

 work like the present, and these have already been 

 described in our articles, Hymenoptera, Cicada, &c. 

 Besides these, the extremity of the abdomen is some- 

 times furnished with additional appendages, such as the 

 forceps of the earwig, common to both sexes (but con- 

 siderably larger in male than the female), and of the 

 scorpion-fly (Panorpa), in which it is only found in the 

 male : the long and slender threads of the may-flies 

 (Ephemera:), which seem to be of service to these 

 injects in their alternate rising and falling flight, 

 being brought into contact when ascending, but ex- 

 panded during the descent; other shorter and broader 

 appendages are found in the dragon-flies, cock- 

 roaches, spectre-insects, &c., sometimes these appen- 

 dages are articulated, at others simple and entire. 



We have now brought our review of the external 

 organisation of insects to a close. That it has ex- 

 tended to a considerable length we are aware, and 

 that it must be to a certain extent comparatively 

 uninteresting to many readers we much fear ; but it 

 appeared impossible to dismiss the subject at shorter 

 length, consistent with the increased number of organs 

 exhibited to us by insects, and which so far exceed 

 those of the higher animals. We have endeavoured 

 as far as possible to keep clear of those minute de- 

 tails which may be said to have reference to a specific 

 instead of a general sketch of entomology. We 

 have, theretore, in the next place, to direct our atten- 

 tion to 



Siib-tection 2. The internal anatomy of insects. 



Having already stated that the skeleton (upon the 

 variations of w Inch much importance is placed in the 

 higher animals), is in insects external, we at once 

 perceive that our labours on arriving at the internal 

 anatomy of the latter have considerably diminished. 



This, indeed, is one of the chief charms of this 

 branch of zoology ; for whilst in the other inverte- 

 brated animals it is almost impossible to preserve the 

 individuals, except in spirits ; and in the vertebrata, 

 except by slutting the skin, whereby the form of the 

 body is entirely dependent upon the fancy of the 

 person who" puts up" the specimen ; insects in almost 

 every instance preserve their form and colour with a 

 freshness often quite equal to the life. It remains 

 for us, therefore, to notice (which we shall do in the 

 most concise manner); the internal systems of sensa- 

 tion, digestion, circulation, respiration, and motion. 

 The generative system, for obvious reasons, will be 

 left untouched by us. 



A The tensitiue or nervous system. The chief 

 means whereby the intercourse of animals with the 

 external world, by the instrumentality of the senses, 



EC T. 



is maintained, is the nervous system, originating in 

 the brain or the spinal cord. 



Hitherto this branch of our subject, and indeed the 

 internal structure of insects in general, has received 

 too little attention from entomologists, of whom we 

 are compelled to say, that mere external form and the 

 collecting of specimens occupy their chief attention. 

 Swammerdam was the first author who carefully 

 traced the nerves of several insects, as the bee, the 

 silkworm, and the Oryctes nasicornis ; but Lyonnet 

 was far more elaborate in performing the same opera- 

 tion in the caterpillar of the goat-moth. More recently 

 Strauss-Durckheim, L. Dufour, and Burmeister, and 

 especially, with reference to its gradational modifica- 

 tion at various periods, M. Herold in the white but- 

 terfly, and our own countryman, Newport, in the 

 Privet Sphinx, have laboured assiduously in the same 

 field. 



144 



Nervous system of the Caterpillar of the Cos.ius ligniperda. The 

 dotted lines indicate the situation of the nerves concealed by 

 the incumbent muscles. 



In insects, as in the other articulated animals, this 

 system is quite unlike that of the higher animals, and 

 consists of two medullary cords or threads, exhibiting a 

 series of knots or ganglions, whereby they are united 

 together at certain distances, occupying the lower sur- 

 face of the internal part of the body, and being defended 

 from the action of the thoracic sternums by the internal 

 Y-like processes above described, as the pro-, meso-, 

 and metathoracic furcae. Sometimes the two gan- 

 glia of each segment are more or less distinct, and 

 sometimes they are united together side by side, oc- 

 cupying the medial line of the body ; and the same 

 occasionally occurs with the communicating threads 

 themselves. The nervous ganglia or knots are 

 placed at more or less equal distances from each 

 other throughout the entire length of the insect, 

 sometime?, indeed, so close, that they constitute but 

 two or more ganglia. 



